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Where to find lightweight 12v batteries?

I need a set of lightweight 12v batteries with a lot of power (15 ah or higher). I have an air conditioner that draws 3.33 amps and runs off 24 volts. My idea is a battery bank with two 12 volts in series to make 24v. I hope to run it ~5 hours off a full charge.

I found these on eBay but they weigh 10lb each, which means 20lb for 2 of them. My goal is 10lb or less total weight:
goo.gl/KcdIfW

A single 15ah+ 24v would work but I cannot find one anywhere.

Thanks!

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-max-17 days ago

Due to the booming "drone" or RC hobby, there is a lot of development in high power density lithium ion / polymer flat-pack cells and multi-cell batteries, just search "LiPo pack"and find ones from reputable/popular companies that meet your needs, and the balancing charger to go along with it.

If you value high energy density over power density (with moderate power density), then 18650 cells simply cannot be beat. LOTS of development has gone into them due to there use in laptops, flashlights, high-powered laser pointers, vaping pens or whatever those are called, Tesla's (electric vehicles in general), power banks, etc etc. You can get Panasonic ones that achieve 3.4AH / cell for about $6 a piece. But if you go with 18650s, then be prepared to search through a minefield of fake 18650's (most of them are generally branded "[something]-fire"). Avoid eBay, Chinese sellers and sites, and have caution on amazon.

You can't beat Lithium cells for lightness, but they are tricky to charge. Look on Ebay or wherever for lithium packs that meet your specification. Don't say "I want this to run at 3 a for 5 hours, so I need 15Ah" - its bad for the batteries to be discharged that far - you'd kill those lead acid cells in 100 charging cycles. You should look for some headroom, for SLA, 50%, I am not sure about Lithiums.

+1 *

* Compared to other tech like NiMh, I wouldn't go so far to say they are tricky to charge (It's just CC then CV @ 4.20v no, dv/dt detection or tempurature monitoring other BS needed) but the tolerances are admittedly pretty tight for safe charging. :)

.... but the tolerances are admittedly pretty tight for safe charging. :)

That's my point...

Even so, I would still consider that "easier" to charge than NiMh or NiCad which for reasonably fast charging requires temperature monitoring(due to the highly exothermic process) and -dv/dt detection, which is IMHO more difficult than what can be achieved with a basic semi-precision lab bench supply or a couple of op amps and trannies; but that's just my humble opinion.

I had mentioned that because I wanted OP to realize that charging techniques for other technologies can also be a little tricky. I would claim that lead acid is the easiest to charge, using the same CC-CV technique as Lithium but not requiring such high tolerances and they are of course more tolerant to abuse.

Unless you want to fast charge, charging the other chemistries is MUCH safer and easier. Nimh / nicadcan be constant current charged at C/10 or slower and lead acid at C/12 or slower can be done just about indefinitely.

The OP didn't give charge rate as a parameter.

I guess you have a point, but I dont know who would want to wait over 10 hours for batteries to charge, and also not have any indication of SoC. :/

+1

benbl19 (author) 17 days ago

Thanks for the suggestions - lithium is a great idea. I decided to go with a pair of 12v lithium batteries that give 14ah, only weighing 2lbs each! Never knew batteries could get so light

Technology is not far enough advanced to provide us with batteries that have no weight, especially when it comes to big power demands.
And even with deep cycle batteries you need at least 30Ah to be on the safe side in terms of discharge voltage and available volts during use.
Even if you take several new laptop batteries I doubt you can be within your weight limit.